Suppression of polycrystal nucleation by methane addition at moderate timing to maintain GaN crystal growth on point seeds in the Na-flux method

• Published in: Journal of crystal growth 2024-02, Vol.627, p.127522, Article 127522
• Main Authors: Hamada, Kazuma, Imanishi, Masayuki, Murakami, Kosuke, Usami, Shigeyoshi, Maruyama, Mihoko, Yoshimura, Masashi, Mori, Yusuke
• Format: Article
• Language: English
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2023.127522

•Crystal nucleation on small PS was inhibited by growth with carbon.•Polycrystals were generated by growth without carbon.•Polycrystal formation was suppressed by adding methane gas at the appropriate timing.•Polycrystal generation was successfully suppressed with methane addition. We have grown low-dislocation, large-diameter GaN substrates using small seed crystals, called as point seeds (PSs) in the Na-flux method. To further reduce dislocation density and improve wafer bowing, reducing the PS diameter is effective. However, it was found that crystals did not start to grow on a small diameter PS. In this study, we also found that a growth on a small diameter PS can be carried out in the condition without graphite addition. However, graphite is conventionally added to suppress polycrystals, so those could not be avoided at the latter process to planarize crystal surface by raising and lowering the crystal, called the flux film coated (FFC) process, in which polycrystals are likely generated. Thus, in this study, we newly proposed to suppress polycrystals by adding methane gas before the FFC process, instead of graphite which cannot be added during the middle of growth.